Melt spinning process and fiber



Patented July 29, 1952 MELT SPINNING PROCESS AND FIBER Harold HenryHeheler, Eggertsville, N. Y., assignor to E. I. du Pont de Nemours andCompany, Wilmington, Del., a corporation of Delaware No Drawing.Application August 23, 1950, Serial No. 181,091

9 Claims.

This invention relates to a process for spinning a synthetic polyesterand is more particularly concerned with a process for melt-spinningpolyethylene terephthalate material to produce tenacious, resilientfibers and yarns.

The preparation of useful textile fibers from synthetic linear polymersof the type first described ;in United States Patents 2,071,250 and2,071,251 to Carothers by previous processes has requiredthe twoseparate operations of spinning and then drawing. Melt-spun fibers ofsynthetic linear polyesters and polyanides in the as-spun state havepreviously been weak and not suitable forv textile uses, except inspecial applications, until drawn. The as-spun tenacities have been inthe range of 0.2 to 0.8 grams per denier, at elongations of severalhundred per cent. By a drawing operation, in which both orientation andcrystallization occur, useful fibers are obtained having tenacities ashigh as 4 to 10 grams per denier. This is generally true for syntheticyarns made from condensation or addition polymers.

It is apparent that considerable economic advantage would be achieved byproviding a process which produces useful as-spun fibers. Elimination'ofthe necessity for a drawing operation subsequent to the normal spinningprocess would result in a considerable saving in both manpower andequipment and would speed up production considerably. Furthermore, for agiven production capacity less space would be necessary, since the floorarea currently needed for drawing yarn would be eliminated.

Considerable research eifort has been directed toward discovering ordeveloping a satisfactory substitute for natural wool. A variety ofsynthetic fibers have been subjected to many different processes, bothmechanical and chemical in an .efliortto so modify their properties thatthey could'take the place of wool. The prior art discusses at greatlength the use Of staple fibermaking equipment and crimpers, as well asvarious chemical and heat-treating methods, for treating syntheticfibers in efforts to secure characteristics normally associated withnatural Wool. However, in no instance have such synthetic materials beenproperly classifiable as wool-like in other than superficial appearance.A great new field of use would be open to a synthetic fiber which couldbe woven into fabrics having the hand, resilience, wrinkle resistance,fullness, warmth and other such properties normally associated with finewoolen fabrics.

It is an object of the present invention to provide a process forspinning fibers and yarns of polyethylene terephthalate material whichare tenacious in the as-spun condition and do not require a subsequentdrawing operation. A further object of the invention is to provideahigh-.- speed process for spinning polyethylene terephthalate fibers oftextile denier and yarns which have the property of spontaneouslycrimping to a tenacious structure having the hand, resilience andwrinkle-resistant characteristics of fine wo'ol when heated in theas-spun condition and.al-, lowed to assume a relaxed condition. Otherobjects of the invention will become apparent from the followingdescription and claims.

The objects of this invention are accomplished by a process whichcomprises extruding a molten fiber-forming material containing at least90 mol percent of polyethylene terephthalate through a spinneret andcooling the extruded material until solidified into fibers whileattenuating the extruded fibers by winding up or forwarding thesolidified fibers to the next operation at .a spinning speed, measuredafter the fibers have completely solidified, or from 3000 to 5200 yardsper minute. The tenacious as-spunfibers or yarns produced spontaneouslycrimp when relaxed and allowed to shrink at a temperature of from about90 to 200 C., to a material having the resilience characteristics offine wool. Preferably the spinning speed is further controlled withinthe above degree of polymerization of the polyester and may be definedas Limit as C approaches 0,

wherein r is the viscosity of a dilute solution of the polyester in amixture of parts phenol and 40 parts tetrachloroethane, divided by; the,

viscosity of the phenol-tetrachloroethane .mix

ture, per se, measured in the same units at the 3 same temperature, andC is the concentration in grams of polyester per 100 cc. of solution.

The fiber-forming material is principally polyethylene terephthalate,but the inclusion therein of up to mol percent of modifying materials isintended whenever the expression polyethylene terephthalatematerial isused. Polyethylene terephthalate itself is a polycondensation product ofethylene glycol and terephthalic acid or an ester-forming derivativethereof.

During the preparation of this polyester, minor amounts of a modifyingmaterial may be added, e. g another glycol and/or another dicarboxylicacid. Thus, a suitable funicular structure comprised essentially ofpolyethylene terephthalate may have included in the polymer molecule upto 10 mol percent of another glycol, such as diethylene glycol,tetramethylene glycol, or hexamethylene glycol. Or again, the moleculemay contain up to 10 mol percent of another acid. As suitable examplesof modifying acids, there may be mentioned hexahydroterephthalic acid,bibenzoic acid, adipic acid, sebacic acid, azelaic acid, the naphthalicacids, 2,5-dimethy1 terephthalic acid and bis-p-carboxy phenoxyethane.

These modifiers may be added as one of the initial reactants during thepolymerization process, but the modifying materials may also bepolymerized separately and then melt-blended with the polyethyleneterephthalate. case the total amount of modifier in the-final polymericmaterial should not exceed 10 mol percent. While the polymerizationprocess is preferfably carried out in the melt, it may also be performedin the solid phase, or in solution or emulsion by conventionalprocedures. An explanation of suitable polymerization processes for thetype of polyesters comprehended herein is contained in United StatesPatent No. 2, l55,319 to Whinfield and Dickson.

In preparing useful resilient yarns by this invention, the followinggeneral procedure is used: The polymer, prepared by a conventionalpolymerization process, is cooled, broken into chips and dried. Thechips are then melted on a heated grid and pumped, by means of ametering pump of the type commonly used in the synthetic textileindustry, through a filter pack and spinneret orifices into roomtemperature air. The extruded filaments cool and solidify by passagethrough the air and are subjected after solidification to a means forforwarding them at spinning speeds in the range of 3000 to 5200 yardsper minute.

By spinning speed is meant the speed of the yarn at a point aftercomplete solidification has occurred, when no more reduction in denieris observed. A convenient point for determining this speed is at thewind-up or forwarding regions. It will be obvious that the speed of anextruded polymer stream will not be the same while in the fiuid orsemi-fluid state as it is at the wind-up or forwarding place.

The means for forwarding the filaments. may comprise a high speed wheel,roll or pinchrolls, an air jet or other suitable means. Under theimpetus imposed by the forwarding means, the filaments elongate in thedistance between the spinneret face and the point of completesolidification. The inertia of the material and the drag of thesurrounding air apparently provide sufiicient drag on the filaments toinduce orientation of the polymer molecules in the solidification range.Actually, no useful orientation takes In either 3 .ments, beginning atthe solidification range.

4 place until the filamentary streams begin to solidify. For severalinches from the spinneret, the filaments appear to be just dangling fromthe spinneret. In the solidification range, the filaments can be seen toaccelerate and become taut. fibers, moving along'their length at highbined filaments from a spinneret are generally forwarded bymeans of anair jet to a high speed cutter, after which the staple fibers are heatedto a temperature of -200 C. in the relaxed state.

All of the fibers and yarns prepared in accordance with the presentinvention are capable of spontaneous crimping. This term is appliedherein to the type of crimp that appears in fibers produced by theprocess of this invention when the fibers are relaxed by heating them toan elevated temperature under little or no tension, and is to bedistinguished from crimp produced bymechanical means. Generallyspeaking, spontaneous crimping is observed when the yarns or fibers areheated to the vicinity of C. within the broader range of 90 to 200 C.previously mentioned.

Suitable heating media include hot air, hot or boiling Water, saturatedor superheated steam, and various hot solutions that exert a mildplasticizing action on the polyester material, e. g., dilute nitricacid. This heat treatment also stabilizes the yarns and increases thedegree of crystallization, while at the same time'reducing residualshrinkage. If desired, the fibers may be forwarded directly from thespinning operation through a suitable bath or a heated chamber andallowed to crimp spontaneously before being wound up or cut into staple.On the other hand, the'fibers can be woven into fabric'and then crimpedspontaneously by heating to 90 to 200 C. as described above. I

r In addition to being wool-like' by virtue of the crimp, yarns andfibers prepared in accordance with the process of this invention possessa property of wool which is most difficult to duplicate, namely,resilience. 'Thisjproperty is not easy to measure quantitatively, butmay be defined to a considerable extent by three important parametersInitia1 tensile modulus, tensile recovery, and compliance ratio. I

p The initial tensile modulus (represented by the symbol Mi) is definedas the slope of the first reasonably straight portion of a stress-straincurve of the funicular structure obtained by plotting tension on avertical axis vs. elongation on a horizontal axis as the structure isbeing elongated at the rate of 10% per minute under a standard conditionof temperature (21 C.) and. humidity (60% RH). In almost every instance,this first reasonably straight portion is also the steepest slope to befound on the curve. The values as used herein are in units of kilogramsper square millimeter per'100% elongation.

The initial tensile modulus, Mi, is a measure of resistance tostretching and bending. The effects of the filament modulus are felt ina fabric chiefly when the fabric is folded or crushed in the hand orotherwise handled. If the modulus is too low, the fabric is "rubbery orlimp; with too high a modulus in the fibers, the fabric is wiry orboardy. When the modulus is in the proper range, a soft fabric results.Attempts have been made to counteract .the efiectsof a modulus lyingoutside the wool range by a suitable adjustment of filament diameter. Ineach instance, this straying away from the usual diameters of woolfilaments has resulted in deleterious effects on properties such asliveliness and recovery from wrinkling. Since the filament propertieswhich are almost entirely responsible for fabric resistance to bendingare (1) the initial modulus and (2) the diameter, and since the range ofsuitable diameters seems to be confined to those typical of Wool, itfollows that a woollike handle will be obtained in the fabric whenfibers having an initial modulus in the wool range are used.

The tensile recovery (TR) defined as the extent to which a yarn recoversits original length after being stretched, a stress-strain curve beingused to determine tensile recovery under the testing conditions. Thetest consists in ex-- tending the funicular structure at a constant rateof elongation of per minute. A specimen is held at the maximumelongation desired for 30 seconds, e. g., by the use of a time switch,and is then allowed to retract at the same rate at which it wasextended. The same specimen is extended approximately 1.0, 3.0 and 5.0%extent for each determination. The extension during elongation and therecovery during retraction are measured along the elongation axis.The-tensile recovery is then the ratio of the extent to which the yarnretracts to the extent to which it was elongated. This test is run understandard conditions at 60% R. H. and 21 C.

It is well known that resistance to wrinkling and mussing and rapidrecovery from unavoidable wrinkles are highly desirable traits inapparel fabrics. The tensile recovery correlates in a high degree withthese properties. The tensile recovery from a 1% elongation correlateswith fabric recovery from mild wrinkling, and, as might be expected, thetensile recovery from higher elongations correlates with recovery frommore severe wrinkling and sharp creasing. In this instance, the wordsresistance to may be used alternatively to recovery from sinceresistance to a crease or wrinkle really involves a very rapid andcomplete recovery from a crease or wrinkle when the deforming force isremoved.

The compliance ratio (CR) is associated with the shape of astress-strain curve and is a measure of the rate of change of compliancewith elongation. Compliance is defined as elongation divided by tensionin kg./mm. Hookean systems, those for which. the stress-strain curve isa straight line, exhibit equal compliance at all elongations: for thesethe change of compliance with, elongation is 0, on the other hand one ofthe most important properties of wool is its change toward highercompliance as it is progressively deformed. It is this property whichenables wool to feel simultaneously crisp and soft This property ismeasured by determining the average rate at which compliance changes inthe range 5 to 10% elongation and is computed by the following formula:

C IO/tension at 10% elongation 5/tension at 5% elongation) Thestress-strain curve of wool has two distinctly different regions,consisting of (1) an initial portion in which the resistance todeformation is relatively great, and (2) a later portion in which theresistance decreases regularly and to a high degree. It is for thisreason that a wool fabric which is crisp and firm to the touch will feelsoft and compliant when severely crushed in the hand. Among the naturalfibers this dualistic behavior is found only in wool and other animalhairs (not in silk, cotton, etc.) and this is one of the most attractiveand valuable characteristics of wool.

In applying the above methods for evaluating wool-like resilience, ithas been found that the better grades of wool for outer garment useshave values for these three parameters in the following ranges Mi=110 to550 kg./mm. CR=0.05 to 0.17 TR=55 or more from extensions of 3 Inaccordance with the process of the present invention synthetic yarns orfibers are produced which have wool-like resilience within the abovelimits. Furthermore the synthetic fibers have these desirable resiliencecharacteristics throughout the fiber length. This is accomplished bymeans of this invention because the filaments receive uniform treatmentthroughout their lengths during formation and subsequent processing.

The spontaneous crimping operation also reduces the tenacity and initialtensile modulus (M1), and increases the compliance ratio (CR). Theeffect on the Mi value becomes important at the higher spinning speeds.Frequently yarns spun at speeds near 5000 yards/minute will initiallyhave values of M1 which are above the desired range. After thespontaneous crimping operation, however, the M1 value will have beendecreased sufiiciently to be within the desired range. This reduction inM1 value may be accentuated by using more severe relaxing conditionsthanwould normally be employed, e. g., steam, glycol, glycerine or mineraloil at l60-200 C., or dilute nitric acid, and/or longer treating times.

The properties of polyethylene terephthalate yarns spun under variousconditions in accordance with the present invention are given in thetable. The general procedure described above was followed, with specificconditions as indicated in the table. In the table, spinning speed is inyards per minute, tenacity is in kilograms per square millimeter and ingrams per denier, and intrinsic viscosity, initial tensile modulus (M1),compliance ratio (CR) and tensile recovery (TR) are as definedpreviously. The physical properties were measured on the crimped fiberafter the fiber samples were boiled in water for an hour. The percentshrinkage was calculated from the difference in length between fibers asspun and after boiling for five minutes in water. This shrinkage relatesthe length of the shrunk crimped fiber bundle to the length of theinitially straight unshrunk fiber bundle and, hence, is a summation ofthe effect produced by the contraction in the length of the fiber bundleand the effect produced by the crimping of the fiber bundle. Examples1-15 inclusive, were carried out using polyethylene terephthalate. InExample 16, a copolymer prepared from ethylene glycol and a :5 mol ratiomixture of terephthalic and sebacic acids was used and, in Examples 17and 18, a similar copolymer containing 10 mol percent of sebacic acidwas used. In Examples 6 to 9, the fibers were crimped by blowing themthrough a pneumatic tube type relaxer fed with air at 150 C. In Examples3, 4, and to 18, the fibers were crimpcd while supported on a movingbelt in an infrared-heated, oven type relaxer.

ages- Staple with less than shrinkage does not crimp well spontaneouslyon relaxed boil-01f. On the other hand, shrinkages much greater than 30%result in very tight wads of staple on batch boil-off that are difiicultto open, although this difficulty can be essentially eliminated byspontaneously crimping the. staple in hot air as it emerges in a fluifystate from the cutter. For

\ Pleiicent R'lensile l m r S Tensile onecovery Ex. I Ii tI iHSC Te m p.Speed Spun Tenacity Strength gation Mi CR from 3 figgfigz CrimpingConditions Viscosity C m f kgJmmJ at percent Break Fxfpnsirm .47 2 5 4300 3.0 2.0 24.4 80 366 0.10 91 Boiling water-l5 min. 3. 58 225 4', 2003. 1 1. 3 15.9 69 159 0.15 83 31 90 C watermin. 0.58 295 4, 300 3. 0 2.0 24. 4 92 231. 0. 10 64 22 150 C air-30 min. 0. 58 295 4, 200 3. 1 2. 22'3. 8 70 366 0. 09 79 30 30 D. S. 1. Steam -5 mm. 0. 60 285 4, 200 2. 92.6 31. 4 105 377 0. 10 83 20 125 C a r-3 mm. 0. 60 280 4, 100 3. 5 2. 834. 2 90 195 0. 05 59 40 150 C a r-5 Sec. 0. 60 280 4, 620 3. 1 2. 9 35.4 82 232 0. 07 67 7 150 C a r-5 sec. 0. 60 280 4, 840 3. 2 3. 0 36. 6 81244 0. 06 02 5 150 C a r-5 sec. 0. 60 280 5, 220 3. l 3. 1 37. 8 76 2420. 06 64 3 150 C a r-5 sec. 0. 60 280 3, 500 1. 6 2. 6 31. 4 102 387 0.09 74 23 125 C air-3 m n. 0.60 280 3,000 l. 2 2.0 24. 4 75 367 0. 08 7027 125 C a r-3 m n. 0. 62 285 4, 300 4. 0 2. 8 34. 2 101 378 0. 10 83 18130 C a1r-4 m n. 0. 62 230 4, 100 5. 9 2. 9 35. 4 86 354 0. 10 81 59 150C air-3 131111. 0. 00 280 3, 800 3. 9 2. l 25. 6 142 208 0. 10 85 150 Ca1r-4 min. 0. 60 280 4, 100 4. 2 2. 9 35. 4 71 390 0.07 94 15 5 p. 5.1.steam-5 min. 0. 59 270 4, 30d 5. 4 2. 7 33. 0 89 378 0. 07 07 30 150 Cair-4 m n. 0. 59 270 3 400 5. 5 l. 7 20. 8 111 244- 0. 14 65 35 150 C ar-4 m n. 0. 59 270 3; 400 4. 3 1. 9 23. 2 200 208 0.16 74 35 150 C air-4min.

Depending upon the exact shrinkage properties of-yarn desired, thespinning speed may be varied within the range of from 3000 to 5200 yardsper minute. The higher spinning speeds result in yarn with lowershrinkage and, conversely, lower spinning speeds result in highershrinkages. Spinning speeds higher than 5200 yards per minute result inhighly oriented, silk-like yarns which do not attain the appearance orresilience characteristics of wool upon hot water or hot air relaxation.Spinning speeds in the range of from 1500 to 3000 yards per minuteresult in lowly oriented yarns, having very high shrinkages andtenacities of around 1.0 to 1.5 grams per denier, which also do notattain wool-like. resilience when crimped. Speeds below 1500 yards perminute do not give yarns useful in the as-spun state, since theyapproach the roperties of conventional unoriented, as-spun polyesters orpolyamides.

.In the range of spinning speeds between 3000 and 5200 yards per minute,the physical properties of the fibers produced are related to the denierof the filaments being spun as well as the spinning speed when thefilament denier is less than three. Spinning speeds near the lower limitof 3000 yards per-minute are preferred for low denier filaments in orderto obtain optimum wool-like resilience characteristics.

The spinning speeds essential in the process of this invention may beobtained by several methods. There may be used a driven bobbin, a highspeed pirn take-up or an air jet may be used as a tensioning andforwarding device wherein the yarn, together with other yarns to form atow, can-be forwarded directly to a staple cutter or to a crimperwithout an intermediate wind-up.

The fibers prepared by means of the process of this invention can becrimped spontaneously by treatment in the relaxed state in water at 90C. to 100 C. Preferably the spinning speed is controlled to give fiberswhich shrink from 15% to 30% when crimped in water at 90 to 100 C.,although, as can be seen from the results given in the table, desirablewool-like resilience characteristics are obtained with much highershrinkany given set of conditions, the spinning speed which will give aspecified shrinkage can readily be determined by adjusting the speedupward if the shrinkage is too great, or downward when the shrinkage istoo little, until the desired shrinkage range is reached.

The fibers of this invention can be crimped spontaneously by treatmentin relaxed condition in hot air at C. to 200 C. Fibers which shrink from15%-30% crimp well when supported on a solid surface, e. g., a movingbelt, in an oven. The preferred method of crimping is to support thefibers by a current of air heated to from 95 C. to 200 C. This method ofcrimping is highly effective and rapid. By this method fibers havingshrinkages as low as 3% and as high as 30% or higher can be crimpedsatisfactorily in a few seconds. A convenient method is to blow staplefibers through a pneumatic tube fed with hot air at a temperature ofabout C.

The molten polymer can be extruded through the spinneret at temperaturesin the range of from 260 to 310 C. For optimum results with polyethyleneterephthalate this extrusion temper ature should be between 280 and 2950., although properties of the final yarn vary but little over theentire range. The preferred temperature range is from 10 to 20 C. lowerwhen copolymers of ethylene terephthalate are used, depending on thecopolymer,and typically in the range of from 270 to 285 C.

When the molten polymer is extruded into room temperature air, theresulting filaments should be allowed to travel at least 45-50 inchesbefore they reach the forwarding means. This distance is required forcomplete solidification. When the distance is in the range of 30-40inches, fused filaments often result with an otherwise standard spinningprocedure because of inadequate quenching time.

The particular fibers prepared by the process of this invention not onlyduplicate fine wool fibers in appearance, but also. in the importantphysical characteristics of initial tensile modulus. tensile recoveryand compliance ratio. As a result, a wool-like fabric may be producedfrom them which is crisp and firm to the touch and. nevertheless, feelssoft and compliant when severely crushed in the hand. These fibers andyarns .of polyethylene terephthalate materials possess,in addition, muchgreater strength and wear resistance than'wool fibers and are notattacked by moths. Fabrics made from these fibers are extremely livelyand wrinkle resistant, with desirable drape and excellent creaseretentivity. They arerem'arkably insensitive to water and changes inhumidity. Also of importance is the versatility which these fiberspossess overand above that of wool for processing into fabrics. They areuseful, particularly in staple form'y'in felts of various kinds,including papermakers felts, carpets, mens and womens suits, bathingsuits, sweaters, knitting yarns, as the warp in Turkish towels and thelike.

Suiting fabrics prepared from the staple fibers produced in accordancewith this invention are particularly outstanding. These are equal to orbetter than high grade woolen suiting fabrics in wrinkle resistance,recovery from wrinkling, and retention of ironed creases. Trousers maybe cleaned by washing in an automatic washer and hanging them up to dry;they do not shrink appreciably, retain their original creases, and needno further pressing.

From the above disclosure it is seen that the present invention providesa high-speed direct method for spinning fibers and yarns of polyethyleneterephthalate materials in a condition in which the fibers or yarns willcrimp spontaneously to desirable resilient structures. The processaccomplishes this result without the necessity of a subsequent drawingoperation. The fibers or yarns may be passed directly from the spinningoperation to the crimping operation to form highly useful fibers oryarns in a continuous operation.

As difierent embodiments of this invention may be made without departingfrom the spirit and scope thereof, it is to be understood that theinvention is not limited to the specific processes disclosed'except asdefined in the appended claims.

What is claimed is:

1. A process for producing tenacious as-spun fibers which comprisesextruding a molten fiberforming material containing at least 90 molpercent of polyethylene terephthalate through a spinneret, cooling theextruded material until solidified to a fiber, and attenuating the fiberin the solidification range by pulling the fiber away from the spinneretat a spinning speed, measured after the material has completelysolidified to a fiber, within the range of from 3000 to 5200 yards perminute, said extruding being at a rate in denyards equal to the productof said spinning speed and the spun denier desired.

2. A process for producing tenacious as-spun fibers which comprisesextruding a molten fiberforming material containing at least 90 molpercent of polyethylene terephthalate through a spinneret, cooling theextruded material until solidified to a fiber, and attenuating the fiberin the solidification range by pulling the fiber away from the spinneretat a spinning speed, measured after the material has completelysolidified to a fiber, within the range of from 3000 to 5200 yards perminute, said spinning speed being further controlled to produce a fiberhaving a shrinkage of from 3% to 30% when immersed in water at atemperature of 90 to 100 C. in a relaxed condition and said extrudingbeing at a rate in denyards equal to the product of said spinning speedand the spun denier desired.

3. A process for producing tenacious as-spun fibers which comprisesextruding, at a temperature in the range of from 260 to 310 C., a moltenfiber-forming material containing at least mol percent of polyethyleneterephthalate through a spinneret, cooling the extruded material untilsolidified to a fiber, and attenuating the fiber in the solidificationrange by pulling the fiber away from the spinneret at a spinning speed,measured after the material has completely solidified to a fiber, withinthe range of from 3000 to 5200 yards per minute, said extruding being ata rate in denyards equal to the product of said spinning speed and thespun denier desired.

4. A process for producing tenacious fibers having wool-like resiliencewhich comprises extruding a molten fiber-forming material containing atleast 90 mol percent of polyethylene terephthalate through a spinneret,cooling the extruded material until solidified to a fiber, andattenuating the fiber in the solidification range by pulling the fiberaway from the spinneret at a spinning speed, measured after the materialhas conpletely solidified to a fiber, within the range of from 3000 to5200 yards per minute, and then heating the fiber to a temperature offrom 90 to 200 C. in a relaxed condition until the fiber hasspontaneously crimped, said extruding being at a rate in denyards equalto the product of said spinning speed and the spun denier desired.

5. A process for producing tenacious fibers having wool-like resiliencewhich comprises extruding a molten fiber-forming material containing atleast 90 mol percent of polyethylene terephthalate through a spinneret,cooling the extruded material until solidified to a fiber, andattenuating the fiber in the solidification range by pulling the fiberaway from the spinneret at a spinning speed, measured after the materialhas completely solidi fied to a fiber, within the range of from 3000 to5200 yards per minute, and then heating the fiber to a temperature offrom 90 to 200 C. while supported by a current of air in a relaxedcondition until the fiber has spontaneously crimped, said extrudingbeing at a rate in denyards equal to the product of said spinning speedand the spun denier desired.

6. A process for producing tenacious fibers having wool-like resiliencewhich comprises extruding a molten fiber-forming material containing atleast 90 mol percent of polyethylene terephthalate through a spinneret,cooling the extruded material until solidified to a fiber, andattenuating the fiber in the solidification range by pulling the fiberaway from the spinneret at a spinning speed, measured after the materialhas completely solidified to a fiber, within the range of from 3000 to5200 yards per minute, and then immersing the fiber in 90 to C. water ina relaxed condition until the fiber has spontaneously crimped, saidspinning speed being controlled to produce a fiber having a shrinkage offrom 15% to 30% in the crimping operation and said extruding being at arate in denyards equal to the product of said spinning speed and thespun denier desired.

7 A process for producing tenacious fibers having wool-like resiliencewhich comprises heating to a temperature of from 90 to 200 C. in arelaxed condition until spontaneously crimped a fiber of polyethyleneterephthalate material formed by extruding the material in a moltencondition through a spinneret, cooling the extruded material untilsolidified to a fiber, and attenuating the fiber in the solidificationrange by pulling the fiber away from the spinneret at a 11 spinningspeed, measured after the material has completely solidified to a fiber,within the range of from 3000 to 5200 yards per minute, said extrudingbeing at a rate in denyards equal to the product of said spinning speedand the spun denier desired.

8. A process for producing tenacious fibers having wool-like resiliencewhich comprises immersing in 90 to 100 C. water in a relaxed conditionuntil spontaneously crimped a fiber of polyethylene terephthalatematerial formed by extruding the material in a molten condition througha spinneret, cooling the extruded material until solidified to a fiber,and attenuating the fiber in the solidification range by pulling thefiber away from the spinneret at a spinning speed, measured after thematerial has completely solidified to a fiber, within the range of from3000 to 5200 yards per minute, said spinning speed being controlled toproduce a fiber having a shrinkage of from 15% to 30% in the crimpingoperation and said extruding being at a rate in denyards equal to theproduct of said spining speed and the spun denier desired.

9. A tenacious as-spun fiber containing at least 90 mol percent ofpolyethylene terephthalate and having the property of spontaneouslycrimping. when heated to a temperature of from 90 to 200 C. in a relaxedcondition, to a crimped fiber having an initial tensile modulus of from110 to 550 kg./mm. a compliance ratio of from 0.05 to 0.17, and atensile recovery of at least 55% from extensions of 3%.

HAROLD HENRY HEBELER.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 20 2,249,756 Finzel July 22, 19412,465,319 Whinfield et a1 Mar. 22, 1949

1. A PROCESS FOR PRODUCING TENACIOUS AS-SPUN FIBERS WHICH COMPRISESEXTRUDING A MOLTEN FIBERFORMING MATERIAL CONTAINING AT LEAST 90 MOLPERCENT OF POLYETHYLENE TEREPHTHALATE THROUGH A SPINNERET, COOLING THEEXTRUDED MATERIAL UNTIL SOLIDIFIED TO A FIBER, AND ATTENUATING THE FIBERIN THE SOLIDIFICATION RANGE BY PULLING THE FIBER AWAY FROM THE SPINNERETAT A SPINNING SPEED, MEASURED AFTER THE MATERIAL HAS COMPLETELYSOLIDIFIED TO A FIBER, WITHIN THE RANGE OF FROM 3000 TO 5200 YARDS PERMINUTE, SAID EXTRUDING BEING AT A RATE IN DENYARDS EQUAL TO THE PRODUCTOF SAID SPINNING SPEED AND THE SPUN DENIER DESIRED.